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5G RailNext: Is 5G connectivity really possible on a train track?

  • 7 minute read
  • Published by Vicki DeBlasi on 4 Jul 2022
  • Last modified 5 Jul 2022
We all know how frustrating it can be when, sitting on a train, you attempt to scroll through your feeds, respond to an email, access your Google drive or even just make a phone call…only to find that your phone signal or the promised Wi-Fi is patchy at best and non-existent at worst.

The challenges in deploying connectivity on mass transit services are complex and varied - from tunnels inhibiting signals to the train carriages themselves which are made of signal-blocking metal and of course, moving at high speeds.   

Then of course we have subway systems; putting those moving carriages underground adds a further complexity to consider.  So should we just accept that underground, tube or subway systems are destined to be connectivity black holes? Well actually, no.  In June 2021, Transport for London announced they had appointed BAI Communications to enable mobile coverage on the whole tube network.  By the end of the year Three and EE had joined the BAI network to provide 4G and 5G-ready mobile connectivity across the London Underground, whilst on the tube and within stations.

The intent to tackle these high profile not spots is clearly there, but how viable is it to deploy 5G in a rail setting?  Step forward 5G RailNext, an international collaboration between the UK and South Korea that aimed to explore exactly that, both from a technical and a commercial perspective. 

What did 5G RailNext Aim to Achieve?

The project set out to explore the viability of 5G in underground transport systems, by deploying and testing it in one of the busiest subways in the world - Seoul - and the third oldest underground metro system in the world - Glasgow.  And to really put it through its paces, it aimed to do much more than ensure people could make a phone call.  Instead, the project team explored the potential to deliver immersive Augmented Reality experiences in an underground train setting, over a 5G network.

The rationale here was two-fold: firstly, this would really test the extent to which the unique characteristics of 5G could be deployed in a mass transit scenario.  Secondly, by looking particularly at immersive experiences, the project endeavoured to explore potential commercial models that could fund such an investment, where transport authorities and operators could both enhance the passenger experience and explore new revenue opportunities, offering brands new marketing channels and an opportunity to deliver immersive and engaging experiences to their customers.  

What did 5G RailNext demonstrate?

The UK team looked at deploying track-to-train connectivity between two stations in the Glasgow subway system, with shared spectrum in the mid-range of frequencies at around 3.5 GHz.

The Glasgow system is a circular 10.5km route with two individual tracks, known as the inner and outer circles.  Trains travel on both circles simultaneously, operating in a clockwise direction for the outer circle and an anti-clockwise direction for the inner circle.

glasgow metro

The subway network was established as a mobile hotspot network where a private 5G network connected platform infrastructure to the trains, which offloaded to an on-carriage Wi-Fi network.

The implementation consisted of three components: the 5G packet core (core network), the Radio Access Network (RAN) and User Equipment (UE).  The trackside RAN infrastructure followed disaggregated and distributed base station architectures, which allowed for greater flexibility in the network design and deployment.  It also allowed for the Remote Radio Head (RRH) to be installed close to the antenna, reducing the amount of cabling required and therefore minimising losses. Maximising the low-loss fibre connection to the Baseband Unit also increased overall performance and energy efficiency by making it easier to maintain optimal distancing between signal source and antenna.

All on-train components were designed to be flexible and easily portable, meaning no components required prior installation on the train. The below diagram shows the subway communication network deployed in Glasgow.

glasgow network

For the trials, live network tests used a carrier bandwidth of 20 MHz, and due to the RF filters of the RRH there was minimal out-of-spectrum band leakage.  This is significant as it means the installed network was extremely unlikely to interfere with other networks operating in the same frequency band, or even with adjacent non-overlapping carriers.  

Testing of the network revealed that a transmit power of 28dBm (0.6W) was enough to secure a good Reference Signal Received Power (RSSP) at all points along the tunnel between Buchanan St and St Enoch stations.  Even at the deepest point of the subway - St Enoch station’s platform at 515m - the RSSP was - 90dBm, sufficient to provide a good data connection.  This transit power was therefore identified as adequate to deliver 5G coverage.  

Latency and throughput measures were also recorded, showing all measurements of latency from the Wi-Fi network to a user device were less than 5ms.  Similar results were obtained for latency between a user device and the on-board edge computer, showing very low level latency communications can be established between a handset and an edge-based content server located on the NUC.

While COVID-19 prevented the project from running trials with subway passengers, smaller-scale trials were conducted with project partners to test the AR experience; the image below showing how passengers could virtually try on a pair of trainers.  These trials successfully demonstrated the ability to deliver a 5G-connected infotainment proposition in an underground rail environment.

trainer try on

What does this mean for the transport sector?

Significantly, the trials demonstrated that 5G can be successfully deployed in an underground metro system, on a moving train.  It appears therefore that 5G technology operating in the mid-range frequency band (~3.5 GHz) is a good fit for delivering track-to-train connectivity.

The commercial model for train operators to invest in 5G connectivity requires further investigation but research conducted by the project with brands to assess levels of interest in developing AR solutions (ranging from immersive brand experiences to virtual shopping), showed that over 85% of respondents had already investigated possibilities but 71% identified consumer readiness to interact with the content as the biggest barrier to deployment.  This would appear to suggest that the market for such content experiences is still in its infancy but brands clearly do expect adoption to increase in the next 2-4 years.  Having said that, it remains clear that connectivity to support AR experiences is also more than suitable to meet more immediate passenger needs such as the ability to stream content and check emails.  The operations of train services can also be aided by 5G connectivity, with the ability to stream ultra-high definition CCTV feeds and the capability to deploy sensors to enable predictive maintenance and improve worker safety (reducing the need for workers to conduct manual checks on live tracks).

Key Learnings

The project identified a number of key learnings that may provide valuable insight to other organisations looking to deploy in a transport setting:

  • Components and installations on rail systems require ‘rail certification’; this needs to be well understood upfront so it can be built into the planning process as it may impact timescales and vendor choices.
  • Installation in a rail environment is complex and time-consuming, having to take place outside of operating hours and requiring numerous approvals.  Installation is therefore likely to take extra time compared to a more traditional environment and this should be factored into planning.
  • Special considerations also need to be given to space and clearance.  In the Glasgow system, tunnels on both lines were only 3.4m in diameter and the track gauge (distance between the inner edges of the rail) only 1.2m.  While clearance between the trains and the tunnel walls varied across the track, it was approximately 10cm in some parts of the network, meaning sizeable telecoms equipment was not an option at those points.  Instead, equipment and antennas could be deployed on areas of the platforms near to tunnel entrances; carefully reviewing the space available will therefore have a significant impact on equipment choice.
  • Train carriages tend to not be permanently coupled, which again needs to be factored into initial design.

For more details on the 5G RailNext project, read the end-of-project report.

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